1. Technical Field
The present disclosure relates to a technology for working against transmission of a fraudulent frame in an in-vehicle network in which electronic control units communicate with one another.
2. Description of the Related Art
In recent years, a plurality of devices called Electronic Control Units (ECUs) have been disposed in a system in motor vehicles. A network that connects the ECUs with one another is called an in-vehicle network. A plurality of standards are provided for in-vehicle networks. One of the mainstream standards is CAN (Controller Area Network) defined by ISO11898-1 (refer to “CAN Specification 2.0 Part A”, [online], CAN in Automation (CiA), [searched on Nov. 14, 2014], the Internet (URL: http://www.can-cia.org/fileadmin/cia/specifications/CAN20A.pdf)).
In CAN, the communication channel is formed from 2 buses. An ECU connected to the buses is referred to as a “node”. Each of the nodes connected to the buses sends and receives a message called a frame. A sender node that sends a frame applies voltages on the 2 buses so as to generate a potential difference between the buses. Thus, the sender node sends a value of “1” called “recessive” and a value of “0” called “dominant”. If a plurality of sender nodes send recessive and dominant at exactly the same time, dominant has higher priority and is sent. If the format of a received frame is abnormal, the receiver node sends a frame called an error frame. An error frame is formed from 6 consecutively sent dominant bits. By sending the error frame, the sender node or the other receiver nodes are notified of the abnormity of a frame.
In addition, in CAN, identifiers indicating the destination address and the source address are not present. The sender node attaches an ID called a message ID to each of frames and sends the frame (i.e., delivers a signal to the buses). Each of the receiver nodes receives only a predetermined ID (i.e., reads the signal from the buses). Furthermore, CAN employs the CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) technique. When a plurality of nodes simultaneously send frames, arbitration using the message IDs is performed, and a frame having a smaller message ID is sent first.
When, in an in-vehicle network, a fraudulent node is connected to the buses and if the fraudulent node unauthorizedly sends a data frame, the vehicle body may be unauthorizedly controlled. To prevent control based on transmission of such a fraudulent frame, a technology for, in general, providing Message Authentication Code (MAC) in a data field defined by CAN and sending the frame has been developed (refer to Japanese Unexamined Patent Application Publication No. 2013-98719).